1. Field of the Invention
The present invention relates to an in-line mixing apparatus, a process for mixing reactive chemical solutions using the apparatus, and a process for producing microcapsules. More particularly, the present invention relates to an improvement of a technique of mixing raw material chemical solutions for a coating solution of pressure-sensitive duplicating paper utilizing microcapsules.
The invention also relates to an in-line mixing apparatus and a process for producing microcapsules, and more particularly, to an improvement of a technique of mixing reactive chemical solutions in an in-line mixing apparatus having a mechanical seal for sealing a rotation shaft of a rotary blade.
2. Description of the Related Art
In the production of pressure-sensitive paper, heat-sensitive paper, a photographic photosensitive material, cosmetics, a paint or the like by utilizing microcapsules, the following procedures are widely employed. A chemical solution containing a polyvalent isocyanate is added to an oil phase solution in which a solute which is to be a core substance of capsules is dissolved in advance, and these are mixed in an in-line mixing apparatus. A water phase solution is then added to the mixed chemical solution, and an oil-in-water emulsion is prepared by agitation. A suitable auxiliary additive, such as a polyvalent amine, is added to the emulsion, and the mixture is subjected to a suitable operation, such as heating, whereby microcapsules having a film, such as a film of polyurethane or polyurea, are prepared. The procedures are described, for example, in Japanese Patent Application Laid-Open (JP-A) No. 5-57178.
In this series of operations, an in-line mixing apparatus is used as the mixing apparatus for mixing the oil phase solution with the chemical solution such as a polyvalent isocyanate to achieve a high throughput in an in-line mixing process over a long period of time, as described in JP-A No. 5-57178. As the in-line mixing apparatus, an in-line mixer can be used, such as a high shearing mixer, a pipeline homo-mixer, a homo-mix line-flow or a fine flow mill.
In the case where a chemical solution of a polyvalent isocyanate and a polyol that reacts with the polyvalent isocyanate is continuously added to and continuously mixed with an oil phase solution that serves as a process fluid, an extremely hard reaction product having a blackish-brown color is formed in an agitation flow path of the in-line mixing apparatus. The reaction product thus formed adheres to and develops on a shaft seal or mechanical seal of a rotation shaft for supporting agitation blades provided in the agitation flow path. Consequently, the function of the shaft sealing portion or mechanical seal is deteriorated, causing such problems as leakage of the liquid from the shaft sealing portion or mechanical seal.
Furthermore, water, which is contained in the oil phase in trace amounts, reacts with the polyvalent isocyanate, and the resultant reaction product adheres to and develops on the shaft sealing portion or mechanical seal of the rotation shaft supporting agitation blades provided in the mixing flow path, so that the function of the shaft sealing portion or mechanical seal is deteriorated, causing such problems as leakage of the liquid from the shaft sealing portion or mechanical seal.
Particularly, in the case where the shaft sealing portion is a mechanical seal, when the reaction product is adhered on a pressing means for pressing a seal ring member to a rotation ring member, the pressing means cannot conform with vibrations caused by high speed rotation of the rotation ring member, and the pressing pressure of the seal ring member to the rotation ring member is decreased, causing leakage of the liquid.
Due to the problems described above, stable operation over a long period of time, which is an intrinsic advantage of continuous mixing by the in-line mixing apparatus, becomes difficult to carry out, and operation shutdown and disassembly for cleaning are necessary after an extremely short period of time. Thus, a considerable reduction in production efficiency is caused.
The invention has been developed under the above circumstances, and an object of the present invention is to provide an in-line mixing apparatus capable of carrying out stable continuous mixing over a long period of time even in the case where chemical solutions having reactivity are mixed, a process for mixing chemical solutions, and a process for producing microcapsules.
According to a first aspect of the invention, there is provided an in-line mixing apparatus for mixing a plurality of chemical solutions, the apparatus including: a mixing apparatus main body, including a plurality of injection inlets and at least one discharge outlet, the plurality of chemical solutions being injected at the injection inlets, the plurality of injection inlets including an upstream injection inlet and at least one downstream injection inlet which are separately disposed; a mixing flow path formed inside the mixing apparatus main body, which communicates with the plurality of injection inlets and the discharge outlet; a rotary blade disposed in the mixing flow path between a vicinity of the downstream injection inlet and the discharge outlet for mixing the plurality of chemical solutions injected at the injection inlets, the rotary blade including a rotation shaft; and at least one of a shaft sealing portion and a mechanical seal disposed at the rotation shaft of the rotary blade for sealing the rotation shaft, the at least one of a shaft sealing portion and a mechanical seal being disposed at a downstream side of the upstream injection inlet and being disposed at an upstream side of the downstream injection inlet, wherein a chemical solution injected at the upstream injection inlet forms a flow along the mixing flow path from the upstream injection inlet to the discharge outlet.
According to the invention, the chemical solution injected into the mixing flow path from the upstream inlet forms a flow from the upstream inlet to the discharge outlet on the mixing flow path, and the rotary blade provided at the downstream side of the shaft sealing portion or mechanical seal. The positional relationship of the flow and the rotary blade can make it difficult for the chemical solution injected into the mixing flow path from the downstream inlet, which is disposed at the downstream side of the shaft sealing portion or mechanical seal, to flow back toward the shaft sealing portion or mechanical seal even when turbulent flow occurs due to the rotation of the rotary blade. Therefore, when a reactive chemical solution is injected from the downstream inlet with respect to the shaft sealing portion or mechanical seal, even if a hard reaction product is formed by mixing of the chemical solutions, almost all of the reaction product does not reach the shaft sealing portion or mechanical seal but is discharged from the discharge outlet. Consequently, deterioration of the function of the shaft sealing portion or mechanical seal due to adhesion of the reaction product to the shaft sealing portion or mechanical seal is not liable to occur, and thus leakage of the liquid from the shaft sealing portion or mechanical seal can be effectively prevented. Thus, stable continuous mixing can be carried out over a long period of time even when chemical solutions having reactivity are mixed.
According to a second aspect of the invention, there is provided an in-line mixing apparatus according to the first aspect, further including a reverse flow preventing mechanism disposed in the mixing flow path between the at least one of a shaft sealing portion and a mechanical seal and the rotary blade, to surely prevent a back flow of the chemical solution injected into the mixing flow path from the downstream inlet toward the shaft sealing portion or mechanical seal.
According to a third aspect of the present invention, there is provided an in-line mixing apparatus according to the second aspect, wherein the reverse flow preventing mechanism includes a weir plate disposed to reduce cross-sectional area of the mixing flow path.
According to a fourth aspect of the present invention, there is provided an in-line mixing apparatus according to the third aspect, wherein the reverse flow preventing mechanism comprises a plurality of the weir plates, wherein the length of the weir plates becomes larger toward the downstream side of the mixing flow path, whereby a flow resistance of the chemical solution injected into the mixing flow path from the upstream inlet is made as low as possible, and thus the back flow of the chemical solution injected from the downstream inlet can be effectively prevented.
According to a fifth aspect of the present invention, there is provided an in-line mixing apparatus according to the fourth aspect, in which the number of the weir plates is from 2 to 10, which is preferable in light of the relationship between the back flow preventing effect and the flow resistance of the chemical solution injected from the upstream inlet.
According to another aspect of the present invention, there is provided an in-line mixing apparatus according to the first aspect, in which the at least one of a shaft sealing portion and a mechanical seal includes: a rotation ring member; a seal ring member; and pressing means for urging the sealing member toward the rotation ring member, and the apparatus further comprises liquid contact preventing means for substantially preventing the chemical solutions in the mixing flow path from coming into contact with the pressing means.
According to still another aspect of the present invention, there is provided an in-line mixing apparatus for mixing a plurality of chemical solutions, the apparatus including: a mixing apparatus main body, including at least one injection inlet, the plurality of chemical solutions being injected at the at least one injection inlet; a mixing flow path formed inside the mixing apparatus main body; a rotary blade disposed in the mixing flow path for mixing the plurality of chemical solutions injected at the at least one injection inlet, the rotary blade including a rotation shaft; a mechanical seal disposed at the rotation shaft of the rotary blade for sealing the rotation shaft, the mechanical seal including a rotation ring member, a seal ring member, and pressing means for urging the sealing member toward the rotation ring member; and liquid contact preventing means for substantially preventing the chemical solutions in the mixing flow path from coming into contact with the pressing means.
According to the invention, the liquid contact preventing means prevents the chemical solutions flowing in the mixing path from coming into contact with the pressing means for pressing the seal ring member of the mechanical seal against the rotation ring member and, whereby the chemical solutions flowing in the mixing path do not reach the pressing means. Consequently, even if chemical solutions having reactivity are mixed in the in-line mixing apparatus, no reaction product is formed that is adhered to the pressing means of the mechanical seal to reduce the pressing force, and thus leakage of the liquid from the mechanical seal can be effectively prevented. Therefore, stable continuous mixing over a long period of time can be carried out even when chemical solutions having reactivity are mixed.
According to still another aspect of the present invention, there is provided the above in-line mixing apparatus, constituted such that a gap, which communicates with the pressing means, is formed between a casing and the seal ring member, and the liquid contact preventing means includes a separating film member which faces the mixing flow path and separates the gap from the mixing flow path so as to prevent the chemical solutions flowing in the mixing flow path from coming into contact with the pressing means. According to this aspect, the pressing means can be physically separated from the agitation flow path, whereby a fundamental solution to the problems of the prior art can be achieved.
According to another aspect of the present invention, there is provided a process for mixing a plurality of chemical solutions, the process including: preparing one of the foregoing in-line mixing apparatuses; and supplying one of the chemical solutions to the downstream injection inlet, the one of the chemical solutions having reactivity with at least one other of the chemical solutions.
According to this aspect, in the case where the plurality of chemical solutions are mixed by using one of the foregoing in-line mixing apparatuses, the chemical solution having reactivity is injected into the mixing flow path from the downstream inlet disposed at the downstream side with respect to the shaft sealing portion or mechanical seal, whereby hardly any of a hard reaction product, if such is formed, reaches the shaft sealing portion or mechanical seal but is discharged from the discharge outlet. Therefore, the reaction product can be prevented from adhering to and growing on the shaft sealing portion or mechanical seal.
According to another aspect of the present invention, there is provided a process for mixing a plurality of chemical solutions including a polyvalent isocyanate and a polyol, the polyvalent isocyanate and polyol being mutually reactive, the process including: preparing one of the foregoing in-line mixing apparatuses; and supplying the polyvalent isocyanate and the polyol to the at least one downstream injection, disposed at a downstream side of the shaft sealing portion or mechanical seal.
According to the aspect, even when an extremely hard reaction product of blackish brown color is formed through a reaction between the polyvalent isocyanate and the polyol, most of a hard reaction product does not reach the shaft sealing portion or mechanical seal but is discharged from the discharge outlet. Therefore, the reaction product can be prevented from adhering to and growing on the shaft sealing portion or mechanical seal.
According to still another aspect of the present invention, there is provided a process for producing microcapsules, the process including: dissolving a solute, which is to be a core material of the microcapsules, in an oil phase solution; mixing the oil phase solution with a polyvalent isocyanate and a polyol in one of the foregoing in-line mixing apparatuses, to form a mixed chemical solution; emulsifying the mixed chemical solution in a water phase solution that includes an emulsifier to form an emulsion; and allowing a polyvalent amine to react with the emulsion to form microcapsules.
According to another aspect of the present invention, there is provided a process for producing microcapsules, the process including the steps of: dissolving a solute, which is to be a core material of the microcapsules, in an oil phase solution; supplying the oil phase solution to an in-line mixing apparatus, which includes sealing means for sealing a rotation shaft of a rotary blade therein, such that the oil phase solution flows along a mixing flow path; supplying a polyvalent isocyanate and a polyol to the in-line mixing apparatus such that the polyvalent isocyanate and the polyol flow the mixing flow path without reaching the sealing means; mixing the oil phase solution, and the polyvalent isocyanate and the polyol to form a mixed chemical solution; emulsifying the mixed chemical solution in a water phase solution which contains an emulsifier to form a emulsion; and allowing a polyvalent amine to react with the emulsion to form the microcapsules.
According to the present invention, when a polyvalent isocyanate and a polyol are mixed in an oil phase solution for production of microcapsules used, for example, in pressure-sensitive paper, heat-sensitive paper, a photographic photosensitive material, cosmetics a paint or the like, stable continuous mixing over a long period of time can be carried out by the use of an in-line mixing apparatus according to the present invention.